1. Field of the Invention
This invention relates to a process for oxidizing sulfur dyes on natural or regenerated cellulose textile fibers. More specifically, the process of the present invention relates to oxidizing sulfur dyes on natural or regenerated cellulose textile fibers with an aqueous solution of hydrogen peroxide and a copper catalyst.
2. Prior Art
Sulfur dyes are generally less expensive than vat dyes in many applications and they are widely used to dye cotton fibers medium to heavy shades of a wide variety of colors. The continuous dyeing operation generally involves impregnating a pre-scoured cotton fabric with a solution of the dye in its reduced form, steaming the impregnated fabric for a short time to increase penetration of the dye into the fibers, washing to remove excess dye then oxidizing the dye on the fabric to render it fast.
Oxidation of reduced sulfur dyes on the fabric is usually effected commercially by a short treatment in a sodium dichromate solution acidified with acetic acid. While such dichromate-acetic acid solutions produce dyed fabrics having good light and wash fastness and wet and dry crock resistance, they nevertheless are unsatisfactory in several respects. Residual chrome salts present in the dyed fibers, even after thorough washing, give the fabric a harsh feel and cause severe friction with over-heating and burning of needles when the dyed fabric is handled on high speed sewing machines and the waste oxidizing solution creates a liquor disposal problem. The liquor disposal problem is particularly troublesome in view of the presence of chromium ions in the waste water. These are toxic and difficult to remove and strict regulations have been proposed by the EPA which limit the amount that can be in the effluent.
Aqueous hydrogen peroxide has not heretofore been regarded as an entirely acceptable replacement for the conventional dichromate-acetic acid oxidizing solutions, since many of the sulfur dyes and notably the sulfur brown or red dyes which are the most difficult to oxidize, are either removed from the fabric by the aqueous hydrogen peroxide solutions before the dye is completely oxidized or are only partially oxidized by the solution with the result that the color intensity of the treated fabric is far from satisfactory.